PeriodicTimer rule (ndis)

The PeriodicTimer rule specifies that the caller of NdisCancelTimerObject must be running at IRQL = PASSIVE_LEVEL if a nonzero value was specified in the MillisecondsPeriod parameter of the NdisSetTimerObject function. If the MillisecondsPeriod parameter of the NdisSetTimerObject function was zero, callers of NdisCancelTimerObject can be running at IRQL <= DISPATCH_LEVEL.